Geology shapes the scenery of the Black Hills, where the northern portion of Custer State Park highlights the granite-rich central core and some of the oldest rocks in North America, more than two billion years old. Formed underground and now exposed at the surface, this dome-like mass of resistant rock reflects a long and complex geologic history that included vast oceans, uplifts, volcanoes, and millions of years of erosion and weathering. The Needles Highway drew public attention after its completion in 1922, and visitors have continued to travel its narrow roadway to enjoy the natural beauty, admire its engineering, and explore recreational opportunities in the rocky terrain. The Needles Eye and Cathedral Spires are granite formations created from magma that cooled very slowly underground, producing large crystals made chiefly of feldspar, mica, and quartz.

Photo: William J. Toman

Photo: William J. Toman

Photo: William J. Toman

Photo: William J. Toman

Photo: William J. Toman

Photo: Mike Stroud

Photo: Mike Stroud

Photo: William J. Toman

Photo: Mike Stroud

Photo: William J. Toman

Photo: William J. Toman

Photo: William J. Toman

Hill City, South Dakota · USA